An electrical discharge machine makes use of a power supply adapted to produce a pulsed electrical discharge repetitively across a dielectric-filled machining gap formed between a tool electrode generally in the form of a solid body (sinking-type EDM) and a wire or the like elongated continuous body (wire-cut or traveling-wire EDM) and a workpiece electrode juxtaposed therewith to impulsively remove a minute volume of material electroerosively from the workpiece while leaving a corresponding crater thereon each time the controlled electrical discharge is effected. As electroerosive material removal proceeds, an electrode-positioning or servo-feed system responds to the gap voltage or other gap variable to maintain the machining-gap size constant while a dielectric-supply unit continuously renews the machining medium which also serves as a coolant in the machining region. The operation is continued until a desired extent of machining or cutting in the workpiece is attained.
Discharge-machined or electroerosively machined surfaces are thus characterized by the peculiarity of an extremely hard "rash" formation or "satin-like" surface formation caused as a result of cumulatively overlapped discharge craters and by their extreme hardness that results from rapid heating and cooling and must generally be smoothed or finished. Furthermore, burrs may be left on the discharge-machined surfaces depending on a shape of the machining electrode used.
Heretofore, while various finishing techniques have been put into practice to finish discharge-machined or electroerosively machined surfaces, they typically require hand operation by the operator after the removal of the workpiece from the EDM unit or installation and have not been satisfactory to efficiently yield finished products which are precision-treated over the entire surfaces.